The present invention relates to a device for admixing an agent in the form of a gas or liquid into a material flow. More particularly, the present invention relates to such a device comprising a chamber, through which the material flow is intended to pass, and means for the supply of gas/liquid to the chamber. More particularly, the present invention relates to such a device intended especially for admixing a gas, such as steam or a bleach gas, into a pulp suspension.
During the treatment of pulp suspensions, various processing agents need to be admixed thereinto, such as for heating or bleaching purposes. It is desired in this connection to atomize the agents in the pulp while the pulp is being transported. For heating the pulp, steam is generally supplied, which condenses and thereby delivers its heat content to the pulp. During bleaching, bleaching agents are added to react with the pulp. In connection with the treatment of recycled fiber pulp, black ink is separated by flotation, implying that air is to be atomized into the pulp.
In all of these cases, it is difficult to achieve uniform admixing. During the heating of pulp by steam supplied to a pulp line, problems are often caused by the formation of large steam bubbles on the inside of the line. When these bubbles rapidly condense, they give rise to condensate bangs, which cause detrimental cavitations in the line and subsequent equipment. It is also difficult to achieve an entirely uniform temperature profile in the pulp. This can be cured by inserting steam supply lines into the pulp line, but this reduces the flow in the line.
For a more uniform admixture of the agent, the material flow can be divided into narrow gaps where the processing agent is supplied. This, however, restricts the capacity and creates a greater risk of clogging. Problems also arise when the material after its passage through the gaps, is again united into a single flow.
The present invention has an object to eliminate the aforesaid problems.
In accordance with the present invention, this and other objects have now been realized by the invention of apparatus for admixing a fluid agent with a flow of material comprising a chamber including an inlet and an outlet, the inlet adapted for connection with an input line for the material having a first predetermined size, and the outlet adapted for connection with an output line for the admixture of the material with the fluid agent and having a second predetermined size, whereby the material can flow through the chamber from the inlet to the outlet, the chamber including a jacket surrounding the flow of the material through the chamber, the inlet defined by an inlet flange and the outlet defined by an outlet flange, the inlet flange defining an opening into the chamber having a third predetermined size smaller than the first predetermined size of the input line, and the jacket including supply means for supplying the fluid agent to the flow of material within the chamber. In a preferred embodiment, the jacket is cylindrical.
In accordance with one embodiment of the apparatus of the present invention, the fluid agent comprises a liquid or gas.
In accordance with another embodiment of the apparatus of the present invention, the material comprises a pulp suspension.
In accordance with one embodiment of the apparatus of the present invention, the jacket has a fourth predetermined size, and the third predetermined size of the inlet flange is smaller than the fourth predetermined size of the jacket.
In accordance with another embodiment of the apparatus of the present invention, the supply means comprises an adjustable gap formed by the jacket, whereby the supply of the fluid agent to the chamber can be controlled. Preferably, the adjustable gap is located at the inlet. In a preferred embodiment, the inlet flange extends into the chamber a predetermined distance to an inner surface of the inlet flange, and the adjustable gap is located immediately outside of the inner surface of the inlet flange whereby an ejector effect is obtained for the fluid agent.
In accordance with one embodiment of the apparatus of the present invention, the supply means comprises a plurality of perforations in the jacket.
In accordance with another embodiment of the apparatus of the present invention, the supply means comprises at least two insert pipes extending through the jacket.
In accordance with another embodiment of the apparatus of the present invention, the apparatus includes a housing enclosing the jacket, thereby defining a space between the housing and the jacket, and including a distributor for the fluid agent comprising the space between the housing and the jacket.
According to the present invention, the processing agent is supplied to a chamber with a cylindrical jacket, through which the material flow passes.
According to the present invention, the material flow passing through the chamber is supplied through an ingoing line and removed through an outgoing line. Due to the reduction in area from the ingoing line to the chamber, according to the present invention a deformation of the flow field of the material flow takes place at the entrance to the chamber. The reduction in area should be from about 10 to 90%, and preferably from about 40 to 60%. This gives rise to shear stresses in the material which have a certain short duration. By utilizing this condition of the material for the admixture of the agent, uniform mixing of atomized agent in the material is obtained.